With the growth of communication networks across the world and with increasing numbers of users, it has become increasingly important to manage bit rates of data transferred across networks. Generally, the transmission of high bit rate data across communication networks consumes significant network bandwidth. Further, with increased data sizes, data storage and efficiency has become an important strategic issue. This is one area where data compression and coding techniques play a significant role. Data compression techniques, which generally include data compression algorithms, help to compress data. By compressing data, it becomes easier to transmit across networks as the compressed data consumes less bandwidth. Further, by using data compression, more data can be stored in limited memory space.
Audio compression is one example of data compression. Audio compression compresses digital audio signals containing speech and finds application in the fields of mobile telephony and voice over IP (VoIP). Encoding techniques for compressing speech signals or audio signals in low bit rates are important to utilize mobile communication system resources effectively. There are speech signal encoding schemes such as G726 and G729 standardized in ITU-T (International Telecommunication Union Telecommunication Standardization Sector). These schemes are targeted for narrowband signals (between 300 Hz and 3.4 kHz), and enable high quality speech signal encoding in bit rates of 8 to 32 kbits/s.
A major disadvantage of existing audio coding systems is that they fail to ensure audio quality when compressing speech. When audio data is compressed to low bit rates, the quality of the audio file gets deteriorated. In order to overcome this limitation, certain audio coding schemes were introduced, of which Code Excited Linear Prediction (CELP) encoding is one of the most popular speech encoding schemes. CELP encoding is a scheme of determining encoded parameters based on a human speech generating model. Most recent standard speech encoding schemes are based on CELP encoding. For example, G.729 enables narrowband signal encoding in bit rates of 8 Kbits/s, and AMW-WB enables wideband signal encoding in bit rates of 6.6 to 23.85 Kbits/s.